10 speed cassette/rear mech compatability

evening gents,

a question for you clever people. Genesis, as yet, have not got back to me with an answer..

my Croix de Fer is 10 speed with 50/34 up front, 12-28 at the back and a Shimano Tiagra 10spd rear mech.

My question is this...what can I take the largest cog at the back up to on that short cage mech?

32, or higher? and what about if I drop the granny down to a 32?

BobCatMax":2w9kvrv4 said:

evening gents,

a question for you clever people. Genesis, as yet, have not got back to me with an answer..

my Croix de Fer is 10 speed with 50/34 up front, 12-28 at the back and a Shimano Tiagra 10spd rear mech.

My question is this...what can I take the largest cog at the back up to on that short cage mech?

32, or higher? and what about if I drop the granny down to a 32?

Click to expand...

Look at something like this:

http://cycle.shimano-eu.com/publish/con ... _road.html

Shimano are pretty good with docs and it says things on them such as max sprocket, sprocket range, and front ring tooth difference.

One thing (supposedly) on some shimano kit is that if you reverse the tensioning screw that adjusts against the drop-out (thread it in from the drop-out side) you can sometimes get a bit more range out of it. Not tried it myself, and not sure it'll work ideally on that rear mech.

D, very informative, thank you.

Still wondering though, if I drop 2 teeth at the front, can I add them at the back. yes, I know the docs say I can't but I don't understand why...

for reference:
Model Number RD-4600-SS
Series TIAGRA
Cassette Compatibility 10
Maximum Sprocket 30T/15T
Minimum Sprocket 25T/11T
Maximum Front Difference 16T
Total Capacity 34T

*edit*

In which case, could I run an MTB rear mech to get a larger spread cassette?

Yes. You could pop a 9 speed mtb rear mech on and run a larger sprocket.

Why would it have to be 9 speed? Do the teeth count on the Jockey wheels matter?

BobCatMax":3jocxlqs said:

D, very informative, thank you.

Still wondering though, if I drop 2 teeth at the front, can I add them at the back. yes, I know the docs say I can't but I don't understand why...

Model Number RD-4600-SS
Series TIAGRA
Total Capacity 34T

Click to expand...

Beacuse you are increasing the range. Your rear mech currently has to be able to keep the chain tensioned in all gears from 34:12 (least chain required) to 50:28 (most chain required). In your new setup the it would be 32:12 (less chain than before) to 50:30 (more chain than before) and the short cage hasn't got enough capacity to cope with that.

Current setup (50+2-(34+12) = 32T
New setup (50+30)-(32+12) = 36T

You could still do it but you'd either have to run the chain too short to be able to use the 50:28 and risk snapping something if you accidently chanaged into that gear, or too long for the 32:12 and have the chain go slack if you accidently put it in that gear.

BobCatMax":25zwxlsw said:

Why would it have to be 9 speed? Do the teeth count on the Jockey wheels matter?

Click to expand...

cos shimano 10 speed mtb mechs use a different cable pull rate to everything else shimano make. And it's ONLY the 10 speed mtb mechs that are different.

JamesM":3tq8bm9p said:

You could still do it but you'd either have to run the chain too short to be able to use the 50:28 and risk snapping something if you accidently chanaged into that gear, or too long for the 32:12 and have the chain go slack if you accidently put it in that gear.

Click to expand...

TBH, the 32/12 ratio is unusable anyway as the chain will always catch on the inside of the 50 ring and rattle like no one's business. I usually look at the 3rd sprocket from top in the working out of capacity (14 or 15?). As that one will usually allow the chain to clear the big ring.

Also, max sprocket size on shimano is always a bit hit and miss. You can very often get away with an extra 2 teeth, depending on how your gear hanger is arranged. If you actually have the hardware kicking around, it's probably worth trying in the workstand first, before buying new bits.

BobCatMax":2mqxwrnd said:

D, very informative, thank you.

Still wondering though, if I drop 2 teeth at the front, can I add them at the back. yes, I know the docs say I can't but I don't understand why...

for reference:
Model Number RD-4600-SS
Series TIAGRA
Cassette Compatibility 10
Maximum Sprocket 30T/15T
Minimum Sprocket 25T/11T
Maximum Front Difference 16T
Total Capacity 34T

*edit*

In which case, could I run an MTB rear mech to get a larger spread cassette?

Click to expand...

If you were set on running bigger cogs at the back, look for the relevant 'GS' rear mech, or, there are 105 and ultegra mid-length cage mechs.

Another thing to consider is that Front Derailleurs only have a certain amount of jump between chainrings they can deal with,so if you went 50 - 32 for example, it may not work (see the specs for the FD in that case).

As said, if you stick the rear derailleur all the way back on its tensioning screw, you might be able to use bigger cogs at the back, but this would mean that the shifting could be potentially less precise as you have adjusted the derailleur thus. Getting a longer cage mech is probably the way forward.

If you really wanted more range, I guess there is always triple? I am guessing you would have to go 32 - 48 at the front or get a different front mech? (All of that starts to add up in costs).

Longer cage (gs/sgs) won't actually give you larger sprockets, just more capacity. It's the mech body (105 vs xt for example) that gives you the larger sprockets.
I *think* that since the event of 10 speed, all road mechs now have the same maximum sprocket size. But it's worth checking.